1. Field of the Invention
The present invention relates to a light-emitting diode (LED) package for a backlight device. More particularly, the present invention relates to a side-emitting LED package having scattering material applied on a reflecting surface, and a backlight device incorporating the LED lens.
2. Description of the Related Art
Applications using a light emitting diode (LED) as a light source are found in an LCD backlight device (system), a lighting device and the like. Also, in broader applications, an optical package may be employed in the LED to further enhance its efficiency and functions.
FIG. 1 shows an example of an LED package for an LCD backlight device.
The LED package of FIG. 1 is a side-emitting LED package 10 comprising a bottom surface 12, a side surface 14 and a funnel-shaped reflecting surface 16. An LED chip 18 is disposed inside the package 10 and the bottom surface 12 of the package 10 is supported by a mount 20 such as a printed circuit board.
The reflecting surface 16 is symmetrical around an axis A such that light generated in the chip 18 is reflected toward the side surface 14. In addition, the center of the LED chip 18 is placed on the axis A. As denoted by reference numeral L1 of FIG. 1, this allows a majority of light generated in the LED chip 18 to be emitted outward through the side surface 14.
However, some portions of light L2, L3 generated in the LED 18 are first reflected from the side surface 14, and then exit upward from the package 10 trough the reflecting surface 16. Alternatively, the light L2, L3 passes through the reflecting surface 16 along the axis line A to exit upward. Also, light L3 generated on an edge of the LED chip is emitted upward from the package through a central portion of the reflecting surface 16.
The light emitted upward radiates in a narrow and strong band. Thus without eliminating it, the LED package 10 is hardly adopted in the LCD backlight device or indirect lighting.
Therefore, to overcome this problem, as shown in FIG. 2, a reflector or reflecting paper 30 is attached to the LED package 10.
The reflecting paper 30 is attached to a top of the LED package 10 to reflect light exiting upward. Light L1, L2 reflected by the reflecting paper 30 enters inside of the LED package 10 again or disappears between a reflecting surface 16 and the reflecting paper 30, or inside the package. This completely blocks light from exiting upward from the package 10, and easily ensures the light to be emitted sideward.
At this time, a bonding section B between the package 10 and reflecting paper 30 is formed on the top of the reflecting surface 18 so that it has a narrow bonding area and thus a weak bonding force. Therefore, for smooth and secure bonding, the package 10 needs to be reconstructed partially. Meanwhile, such reflecting paper attached may lead to undesired reflection of light L3.
To attach the reflecting paper is a delicate manual job that can be hardly automated, thus increasing the manufacture time and cost for the backlight device. Moreover, the reflecting paper attached easily falls off, undermining reliability of the backlight device.
Problems arise when the structure of FIG. 2 is applied to the backlight device. An explanation thereof will be given hereunder with reference to FIG. 3.
As shown in FIG. 3, a direct-type backlight device 40 comprises a flat reflecting plate 42, side-emitting LED packages 10 as described in FIGS. 1 and 2 installed on the reflecting plate 42, reflectors or reflecting papers 30 disposed on the LED packages 10 as stated with reference to FIG. 2, a transparent plate 44 positioned at a predetermined distance G1 from the reflecting papers 30 and a diffuser plate 46 positioned at a predetermined distance G2 from the transparent plate 44.
The LED package 10 generally emits light L1, L2 sideward. The light L1 emitted is reflected from the reflecting plate 42, and passes through the above-disposed transparent plate 44. Thereafter, the light L1 is diffused at a desired uniform intensity in the above-disposed diffuser plate 46 and provides a backlight to a liquid crystal panel 48 disposed above. Another light L2 strikes a bottom of the transparent plate 44 and some portions of the light L21 enter the transparent plate 44 and provide a backlight to the liquid crystal panel 48 through the above-disposed diffuser plate 46.
Meanwhile, other portions of the light L22 are reflected from the transparent plate 44 to the reflecting plate 42 and then reflected onto the reflecting plate 42. Then the light L22 provides a backlight to the liquid panel 48 through the transparent plate 44 and diffuser plate 46 in the same manner as the light L1 does.
The backlight device 40 of this structure enables an array of LED packages 10 to be installed below the liquid panel 48, advantageously ensuring an efficient supply of a backlight to a large-sized LCD.
However, a predetermined distance G1 is required between the LED package 10 and the transparent plate 44 and also a predetermined distance G2 should be kept between the transparent plate 44 and the diffuser plate 46. Disadvantageously, this increases a thickness of the backlight device 40 of this structure.
Specifically speaking, light L generated in the LED package 10 is generally reflected upward through between the reflecting papers 30, thus forming dark areas DA shaded by the reflecting papers 30 on the transparent plate 44. To eliminate the dark areas DA and resultant bright lines, a predetermined distance G2 or more should be sufficiently maintained between the transparent plate 44 and the diffuser plate 46 so that lights mix together until before passing through the transparent plate 44 and entering the diffuser plate 46.
As described above, to ensure light traveling from the reflecting plate 32 to the liquid crystal panel 48 to radiate at a uniform intensity, such predetermined distances G1, G2 or more should be maintained, which however necessitates an increase in a thickness of the direct-type backlight device 40.